Add support for profiling benchmarks using perf-record

[mpage]

This PR adds support for profiling benchmarks using a perf-record hook. perf-record is enabled only during benchmark execution by using perf's support for control fifos.

For example, to collect stacks using DWARF debug information, one could run:

env PYPERF_PERF_RECORD_EXTRA_OPTS="--call-graph dwarf -e cycles:pp" \
       python -m pyperf timeit \
                    --debug-single-value \
                    --hook perf_record \
                    --inherit-environ PYPERF_PERF_RECORD_EXTRA_OPTS \
                    '1+1'

This should resolve #213.

[corona10]

I will try to take a look at it by this weekend :)

[mdboom]

Thanks for doing this. This is a tricky one to add a test and CI for -- I did test it locally and it "worked for me". I think for most purposes we can rely on bench_runner to ensure this doesn't bit rot.

[corona10]

Would you like to update the documentation for it? https://github.com/psf/pyperf/blob/f3131745472b108b95cd5e20733cdf4a20ec0a37/doc/run_benchmark.rst#specializer-statistics-pystats

[mdboom]

@mpage: Are you working on addressing @corona10's comments? If not, just let me know and I can handle. I'd like to see this merged as well ;)

[mpage]

Ahh, thanks for the nudge. I've been heads down finishing up the LOAD_FAST optimization. I should be able to wrap this up on Friday.

[mpage]

@mdboom @corona10 - Sorry about the delay! I think I've addressed all the review comments and updated the docs.

[corona10]

lgtm